Checkbox:

value: The submit value of the field when it is checked.

uncheckedValue: The submit value of the field when it is unchecked.

defaultChecked: Indicates if the checkbox is checked.warning:: When setting “defaultChecked” = “true”, you have to set the value of “uncheckedValue” so that the form values will be always populated.
Otherwise Sling Post Servlet will remove the property from the form values, which makes the checkbox to be always checked.